Cuprate Oxyfluorides La2Cu0.8Ni0.2O3F2 and La2CuO3F2 with Channel-like Anion Ordering

Highly fluorinated cuprate Ruddlesden-Popper oxyfluorides La2Cu0.8Ni0.2O3F2 and La2CuO3F2 were obtained by topochemical reaction between poly(vinylidene fluoride) (PVDF) and the corresponding oxides La2Cu0.8Ni0.2O4 and La2CuO4 prepared by citrate-based soft chemistry synthesis. The crystal structures of both oxyfluorides were investigated by powder diffraction techniques. The structure of La2Cu0.8Ni0.2O3F2 was solved based on combined neutron and X-ray powder diffraction. It crystallizes in a new monoclinic distorted version [C2/c a = 13.1880(3) angstrom, b = 5.7244(1) angstrom, c = 5.6007(1) angstrom, and beta = 90.85(1)degrees] of the anionic ordered structure lately reported for La2NiO3F2. For La2CuO3F2, an even less symmetrical triclinic structure was derived from X-ray powder diffraction data [P (1) over bara 5.6180(5) angstrom, b = 5.7316(6) angstrom, c = 7.1978(9) angstrom, alpha = 113.32(1)degrees, beta = 90.89(9)degrees, and gamma = 90.16(11)degrees]. For both compounds, an additional tilt component of the partially Jahn-Teller elongated (Cu,Ni)O4F2 octahedra was found as the origin for the lowered symmetry. The formation reaction of La2CuO3F2 was studied by in situ XRD measurements. In these investigations, two new reaction intermediates were identified. The magnetic properties of both oxyfluorides La2Cu0.8Ni0.2O3F2 and La2CuO3F2 were characterized by field-and temperature-dependent measurements. An antiferromagnetic ordering with TN = 240 K was found for La2Cu0.8Ni0.2O3F2. In La2CuO3F2, additional weak ferrimagnetism was observed, resulting in a pronounced hysteresis but a weak saturation moment, which was attributed to result from a canted antiferromagnetic spin arrangement.

Automated summary

Highly fluorinated cuprate Ruddlesden-Popper oxyfluorides La2Cu0.8Ni0.2O3F2 and La2CuO3F2 were obtained by topochemical reaction. The crystal structures of both oxyfluorides were investigated, and the reasons for the lowered symmetry were found. The formation reaction of La2CuO3F2 and its reaction intermediates were studied. La2Cu0.8Ni0.2O3F2 showed antiferromagnetic behavior, while La2CuO3F2 exhibited weak saturation moment and weak ferrimagnetic properties.